Gas turbine engines generally include a high pressure compressor for compressing air flowing through the engine, a combustor in which fuel is mixed with the compressed air and ignited to form a high energy gas stream, and a high pressure turbine. The high pressure compressor, combustor and high pressure turbine sometimes are collectively referred to as the core engine. Such gas turbine engines also may include a low pressure compressor, or booster, for supplying compressed air, for further compression, to the high pressure compressor.
If the disk rim temperature in the high pressure turbine approaches operational limits, rim cavity cooling systems are necessary. Low friction devices such as windage covers and straight or step-up seals have been used to control cooling temperatures and thereby protect critical components from increasingly severe engine cycle conditions. In addition, a combination of forward outer seal (FOS) flow and FOS bypass flow have been used to supply the forward rim cavity with reasonably cool air. The FOS bypass flow is effective because such flow is not affected by the friction heating in the seal. Such bypass flow, however, reduces performance of the high pressure turbine and high pressure turbine blade cooling flow.
FIG. 1 is a schematic illustration of a portion of a CFM56 turbine 10 including a known blocker hole configuration. Turbine 10 includes rotating components 12 and stationary components 14 as is known. One of rotating components 12, for example, is a seal 16. A plurality of flow paths extend through at least portions of turbine 10, such as a forward outer seal (FOS) flow 18 and a FOS bypass flow 20. Flow path 18 extends, for example, through a first swirling cavity 22 between seal 16 and stationary components 14 to a forward rim cavity 24. Air is supplied to flow path 18 from both seal compressor delivery pressure (CDP) exit air 26 and nozzle cooling air 28. Air is supplied to FOS bypass flow from CDP seal exit air 26.
As shown in FIG. 1, a blocker hole 30 is formed in stationary component 14, and seal exit air 26 flows through blocker hole 30 into first swirling cavity 22. Airflow through blocker hole 30 provides back-pressure to seal 16 and limits the leakage of high pressure turbine blade cooling air through seal 16. In practice, and in the CFM56 turbine, a plurality of blocker holes 30 are provided.
Airflow through blocker holes 30, however, results in injecting unswirled air into first swirling cavity 22. As a result, rotating seal 16 imparts more net torque on, and therefore more heat into, the cavity air. Injecting more heat into the cavity results in reducing the performance of the high pressure turbine and high pressure turbine blade cooling flow.
As performance targets become more aggressive, the FOS bypass flow must be reduced or eliminated. Of course, reducing or eliminating such flow should not adversely affect satisfying the cooling requirements.